711 research outputs found
GMC Collisions As Triggers of Star Formation. IV. The Role of Ambipolar Diffusion
We investigate the role of ambipolar diffusion (AD) in collisions between
magnetized giant molecular clouds (GMCs), which may be an important mechanism
for triggering star cluster formation. Three dimensional simulations of GMC
collisions are performed using a version of the Enzo magnetohydrodynamics code
that has been extended to include AD. The resistivities are calculated using
the 31-species chemical model of Wu et al. (2015). We find that in the
weak-field, case, AD has only a modest effect on the
dynamical evolution during the collision. However, for the stronger-field,
case involving near-critical clouds, AD results in formation
of dense cores in regions where collapse is otherwise inhibited. The overall
efficiency of formation of cores with in
these simulations is increases from about 0.2% to 2% once AD is included,
comparable to observed values in star-forming GMCs. The gas around these cores
typically has relatively slow infall at speeds that are a modest fraction of
the free-fall speed.Comment: 15 pages, 15 figures, Accepted to Ap
GMC Collisions As Triggers of Star Formation. IV. The Role of Ambipolar Diffusion
We investigate the role of ambipolar diffusion (AD) in collisions between
magnetized giant molecular clouds (GMCs), which may be an important mechanism
for triggering star cluster formation. Three dimensional simulations of GMC
collisions are performed using a version of the Enzo magnetohydrodynamics code
that has been extended to include AD. The resistivities are calculated using
the 31-species chemical model of Wu et al. (2015). We find that in the
weak-field, case, AD has only a modest effect on the
dynamical evolution during the collision. However, for the stronger-field,
case involving near-critical clouds, AD results in formation
of dense cores in regions where collapse is otherwise inhibited. The overall
efficiency of formation of cores with in
these simulations is increases from about 0.2% to 2% once AD is included,
comparable to observed values in star-forming GMCs. The gas around these cores
typically has relatively slow infall at speeds that are a modest fraction of
the free-fall speed.Comment: 15 pages, 15 figures, Accepted to Ap
A novel strategy for the targeted analysis of protein and peptide metabolites
The detection and quantitation of exogenously administered biological macromolecules (e.g. vaccines, peptide and protein therapeutics) and their metabolites is frequently complicated by the presence of a complex endogenous mixture of closely related compounds. We describe a method that incorporates stable isotope labeling of the compound of interest allowing the selective screening of the intact molecule and all metabolites using a modified precursor ion scan. This method involves monitoring the low molecular weight fragment ions produced during MS/MS that distinguish isotopically labelled material from related endogenous compounds. All isotopically labelled substances can be selected using this scanning technique for further analysis whilst other unlabelled and irrelevant substances are ignored. The potential for this technique to be used in metabolism and pharmacokinetic experiments is discussed with specific examples looking at the metabolism of α-synuclein in serum and the brain
GMC collisions as triggers of star formation â VIII. The core mass function
Compression in giant molecular cloud (GMC) collisions is a promising mechanism to trigger the formation of massive star clusters and OB associations. We simulate colliding and non-colliding magnetized GMCs and examine the properties of pre-stellar cores, selected from projected mass surface density maps, including after synthetic ALMA observations. We then examine core properties, including mass, size, density, velocity, velocity dispersion, temperature, and magnetic field strength. After 4 Myr, âŒ1000 cores have formed in the GMC collision, and the high-mass end of the core mass function (CMF) can be fit by a power-law dN/dlogM â M-α with α â 0.7, i.e. relatively top heavy compared to a Salpeter mass function. Depending on how cores are identified, a break in the power law can appear around a few
710 Mâ. The non-colliding GMCs form fewer cores with a CMF with α â 0.8â1.2, i.e. closer to the Salpeter index. We compare the properties of these CMFs to those of several observed samples of cores. Considering other properties, cores formed from colliding clouds are typically warmer, have more disturbed internal kinematics, and are more likely to be gravitational unbound, than cores formed from non-colliding GMCs. The dynamical state of the protocluster of cores formed in the GMCâGMC collision is intrinsically subvirial but can appear to be supervirial if the total mass measurement is affected by observations that miss mass on large scales or at low densities
What Influences Employees to Use Enterprise Social Networks? A Socio-Technical Perspective
The adoption of enterprise social network (ESN) for greater employee engagement and knowledge sharing practices within organisations is proliferating. However, ESN investments have thus far not resulted in expected gains in organisational benefits due to underutilisation by employees. Limited understanding of the implications of ESN use leads to a paucity of recommendations for effective use within an organisation. This research-in-progress paper seeks to determine the factors influencing the use of ESN among employees in a large Australian utility organisation, with the aim of contributing to a practical understanding of the key success factors of the use of this new workplace social platform. Our preliminary findings indicated that the employeesâ ESN behaviour tends to be influenced by socio-technical factors, including technological (i.e. platform and content quality), organisational (i.e. top management support and ESN facilitating conditions), social (i.e. critical mass and communication climate), individual (i.e. perceived benefits, knowledge self-efficacy and time commitment) and task (i.e. task characteristics) factors. This paper concludes that a successful implementation of ESN in an organisation involves the nexus between these five factors and provides several recommendations about how ESN use can be enhanced
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